1. Field of the Invention
The present invention relates to substrate surface alignment techniques and, more particularly, to a method for fabricating liquid crystal (LC) alignment.
2. Description of the Prior Art
With the advances in Internet and video technology, use of flat panel displays is becoming more important and essential to people's daily life. Unlike conventional CRT panel televisions, liquid crystal displays (LCD) have advantages, such as light, compact, full-color display, radiation-free, digital, high-definition, and power-saving, and thus liquid crystal displays seemingly become the potential mainstream flat panel displays of the next generation.
For liquid crystal displays, the transmission paths and phases of light are altered through the control over the geometric changes of liquid crystals by electric field. With polarizers, liquid crystal displays achieve contrast, which, coupled with driving circuits and color filters, account for the gray scale and colors displayed. In this regard, liquid crystal (LC) alignment technique plays an important, key role in a liquid crystal panel process. The liquid crystal alignment process is not only crucial to the control of the arrangement and alignment of liquid crystals but also indispensable to high-quality display features, such as viewing angle, response time, contrast, and color.
With the advances in the liquid crystal display process technology and the decrease in product costs, it is foreseeable that in the near future liquid crystal display television (LCD TV) will become an information appliance (IA) indispensable to every family. Hence, manufacturers nowadays are devoted to LCD TV research. At present, there are two intractable issues about the liquid crystal displays for use in TV, namely wide viewing angle and short response time.
Major wide-angle technologies in use are, namely Twisted Nematic (TN), Super Twisted Nematic (STN), Multi-domain Vertical Alignment (MVA), and In-Plane Switching (IPS). Unsatisfied with the existing response time, some propose the Optically Compensated Bend (OCB) technique. With the OCB technique, both wide viewing angle and short response time are achievable goals. As regards wide viewing angle, in the presence of an optimized retarder, the viewing angle can be increased to 140° vertically and 160° horizontally, and the response time is less than 7 ms for full gray scale and even less than 3 ms for 15.2″ panel. Besides, inasmuch as the OCB technique enables liquid crystal molecules to be disposed in an arch-shaped pattern, animations with little image sticking can be displayed even at low temperature, and the response time is as short as 40 ms even at a low temperature as low as −20° C., and thus OCB-mode LCD is ten times faster than other types of LCD in terms of low-temperature response time.
Despite its advantages like wide viewing angle and short response time, OCB-mode LCD does have its own drawbacks. For instance, in order to switch an alignment state of liquid crystal molecules from splay alignment to bend alignment, and allow the liquid crystal molecules to continue with the bend alignment without returning to radial alignment, the liquid crystal molecules have to be aligned at different pretilt angles in accordance with their respective compensated angles, and thus splay-bend transition takes place. Owing to the elastic energy of liquid crystal molecules, formation of splay alignment is fast. However, once the bend alignment starts to recur, those liquid crystal molecules with relatively high pretilt angles (for example, from 45° to 55°) will become unstable, which is exactly the point where there is the greatest difficulty in mass production based on the OCB technique.
In order to solve the aforesaid problem, related technologies in use involve using a combination of vertical polymer alignment film and horizontal polymer alignment film to fabricate a microstructured surface. In order to solve interface-related problems arising from the combination of two markedly different polymers, the related technologies in use involves providing a substrate 5 formed with a conductive layer 51 and an alignment film 53 as shown in FIG. 7A, and performing an alignment rubbing process on the alignment film 53 with a view to aligning liquid crystal molecules as shown in FIG. 7B, such that the liquid crystal molecules are aligned in the same direction as shown in FIG. 7C.
However, alignment rubbing is unreliable whenever a high pretilt angle is involved. In the alignment rubbing process, rubbing of alignment film brings about dust, electrostatic charges, and rubbing defects, thus reducing the yield and the reliability of the process. Hence, there is still room for improvement in the prior art.
For the aforesaid reasons it is highly desirable to develop non-rubbing alignment techniques. Non-rubbing alignment research nowadays is mainly directed to three techniques, namely photoalignment, ion beam alignment, and plasma beam alignment.
Photoalignment is good at homogeneity, but it has technical bottleneck which calls for a breakthrough in such areas as anchoring energy and image sticking. Also, its stability depends on the life of the bulb of the exposure equipment used as well as flashing of a light source.
Ion beam alignment technology requires high-vacuum equipment and electrostatic charge removing equipment and therefore incurs high costs, not to mention that the life of the ion gun used remains an intractable problem. Hence, at the present moment ion beam alignment technology is still limited to laboratories.
Referring to FIG. 8, plasma beam alignment technology involves generating a single plasma beam 61 by a single plasma generating device 6 disposed in a process space, and scanning to and fro an alignment film of a substrate 63 vertically so as to achieve alignment. Although products manufactured by plasma beam alignment technology are almost up to standard, their mass production is faced with such problems as a long process and poor adjustment of direction, because a single plasma generating device has to scan an alignment film to and fro. Besides, scanning back and forth generates vibration that brings about the instability of a process.
Accordingly, an issue calling for urgent solution involves coping with the problems facing the prior art.